What Are the Symptoms of Magnesium Deficiency? Who Is at Risk?

In brief:

• Adult women need 310–320 mg of magnesium daily; requirements increase in pregnancy.
• These symptoms occur in many other conditions, so they do not indicate deficiency on their own.
• Blood magnesium does not fully reflect total body magnesium; assessment is a doctor's responsibility.
• The adult upper limit for supplemental magnesium is 350 mg a day; excess amounts may cause diarrhoea, nausea and abdominal cramps.

What does magnesium do?

Magnesium is needed for more than 300 enzyme systems in the body. It plays a role in muscle and nerve function, blood sugar and blood pressure regulation, energy production and bone structure. It is also needed to make DNA and RNA (NIH).

For the different forms of magnesium, such as bisglycinate, citrate and malate, see Is All Magnesium the Same? What Does Each Form Do?. We summarise research on magnesium and other supplements for PMS in What Is PMS?.

What are the symptoms of magnesium deficiency?

According to the NIH fact sheet:

Early symptoms:

• Loss of appetite
• Nausea and vomiting
• Tiredness
• Weakness, lack of strength

As deficiency progresses:

• Numbness
• Muscle contractions and cramps
• Abnormal heart rhythms
• Seizures

Severe deficiency may also lower calcium and potassium levels in the blood.

None of these symptoms is specific to magnesium deficiency. Tiredness or muscle cramps may have many other causes. If symptoms persist, it is better to see a doctor than to start a supplement on your own.

Who is at risk of magnesium deficiency?

The NIH identifies these groups as being at higher risk of magnesium inadequacy:

• People with digestive diseases, such as coeliac disease or Crohn's disease
• People with type 2 diabetes
• People with alcohol dependence
• Older adults

Some medicines can also lower magnesium levels (NIH):

• Proton pump inhibitors that reduce stomach acid: usually when used for longer than a year
• Some diuretics: they may increase magnesium loss in urine

If you have been taking one of these medicines for a long time, discuss your magnesium level with your doctor.

How much magnesium do you need each day?

According to the NIH, women's daily requirements are:

Many people do not obtain this amount from food. A US national survey (NHANES 2013–2016) found that 48% of people across all ages consumed less magnesium from food than required (NIH).

Which foods contain magnesium?

Nuts, seeds, pulses, green leafy vegetables and whole grains are good sources. Some examples from the NIH food table, per serving:

• Roasted pumpkin seeds, 28 g: 156 mg
• Chia seeds, 28 g: 111 mg
• Roasted almonds, 28 g: 80 mg
• Boiled spinach, half a cup: 78 mg
• Roasted cashews, 28 g: 74 mg
• Peanuts, a quarter of a cup: 63 mg
• Soya milk, 1 cup: 61 mg
• Boiled black beans, half a cup: 60 mg
• Peanut butter, 2 tablespoons: 49 mg
• Baked potato with skin, 100 g: 43 mg
• Boiled brown rice, half a cup: 42 mg
• Plain low-fat yoghurt, 225 g: 42 mg
• A medium banana: 32 mg

Magnesium from food does not cause problems in healthy people; the kidneys remove the excess (NIH).

How is magnesium deficiency identified?

Most body magnesium is inside cells and bones, which makes its level difficult to measure. The most common method measures magnesium in the blood. However, this does not fully reflect total body magnesium or the amount in tissues. A full assessment may require a medical examination alongside laboratory tests (NIH).

What should you consider when taking magnesium supplements?

• Upper limit: For adults, the upper limit for magnesium from supplements and medicines is 350 mg a day. High doses can cause diarrhoea, nausea and abdominal cramps; very high doses can be dangerous (NIH). This limit does not include magnesium in food.
• Kidney disease: When kidney function is impaired, excess magnesium cannot be removed, increasing the risk of toxicity (NIH). If you have kidney disease, do not use a supplement without consulting your doctor.
• Medicine interactions: Magnesium can reduce absorption of bisphosphonates used for osteoporosis and certain antibiotics. These antibiotics should be taken at least 2 hours before or 4–6 hours after a magnesium supplement (NIH).
• If you take regular medication, consult your pharmacist before starting a supplement. We explain how supplements differ in Do All Food Supplements Have the Same Effect?.

When should you see a doctor?

• If tiredness, weakness or cramps have persisted for a long time
• If you have numbness, tingling or palpitations
• If you have used a proton pump inhibitor or diuretic for a long time
• If you have a digestive disease, diabetes or kidney disease and are considering a supplement

Frequently asked

Can a blood test detect magnesium deficiency?

A blood test is the most common method, but does not fully reflect total body magnesium. A doctor assesses the result alongside symptoms and an examination (NIH).

Is too much magnesium from food harmful?

Not in healthy people; the kidneys remove excess magnesium in urine. The upper limit applies only to magnesium from supplements and medicines (NIH).

Which medicines lower magnesium?

Long-term proton pump inhibitors, used to reduce stomach acid, and some diuretics may lower magnesium levels (NIH). Do not stop your medicine on your own; speak to your doctor.